Effect of irrigation and tourniquet application on aminoglycoside antibiotic concentrations in bone

Bone gentamicin concentration after intra-articular injection or regional intravenous perfusion in the horse

OBJECTIVE

To compare intra-articular (IA) and bone gentamicin concentrations achieved after intra-articular administration or regional intravenous perfusion (RIP).

STUDY DESIGN

Experimental study.

ANIMALS

Twelve healthy adult horses.

METHODS

Horses were assigned to 2 treatment groups (n = 6/group): Group 1, 1 g gentamicin administered simultaneously in both left and right metacarpophalangeal joints and group 2, 1 g gentamicin administered simultaneously in both left and right lateral palmar veins. Serum, synovial fluid, and bone biopsy specimens were collected. Gentamicin concentrations were determined by fluorescence polarization immunoassay. Bone, synovial fluid, and serum gentamicin concentrations were compared over time and between groups using 2-way ANOVA. Significance of all tests were evaluated at P <.05.

RESULTS

IA metacarpophalangeal joint administration resulted in higher concentration of gentamicin in synovial fluid than RIP administration. Synovial fluid concentration remained above minimum inhibitory concentration (MIC) for common pathogens for over 24 hours with IA and RIP administration. Bone gentamicin concentration remained above MIC for 8 hours with both methods; there was no significant difference in gentamicin concentration in bone with either method. Neither IA nor RIP administration had a significant effect on serum concentration of gentamicin.

CONCLUSIONS

In normal horses, there is no difference in bone gentamicin concentration obtained with IA or RIP administration.

CLINICAL RELEVANCE

Based on MIC for common equine pathogens, administration of gentamicin intra-articularly or by regional intravenous perfusion should be useful for treatment of osteomyelitis.

Removal of surface bacteria by irrigation

We examined the efficacy of various irrigation solutions delivered through a power irrigator to remove bacteria from three different surfaces. Titanium, stainless-steel, and cortical bone surfaces were coated with three different bacterial species: Staphylococcus aureus, Pseudomonas aeruginosa, and Staphylococcus epidermidis. They were then irrigated with 1 L of fluid delivered by jet lavage. The fluids tested were normal saline and solutions of bacitracin, neomycin, and soap. One set of specimens was not irrigated, as a control. After irrigation, the specimens were sonicated to remove residual bacteria, and the sonicate was quantitatively cultured to allow evaluation of the amount of residual bacteria on the surface. The results showed that removal of bacteria reflects an interaction between bacterial species, surface characteristics, and irrigation solution. Fewer bacteria were present in all the irrigation groups than in the control. Soap solution was as good as or better than any other solution at removing all three types of bacteria from all three surfaces, although not all of the pairwise comparisons were statistically significant. There was a significant advantage to soap solution over antibiotic irrigant or saline alone in removing Staphylococcus epidermidis from metallic surfaces. The use of soap solution for irrigation seems to improve the removal of some bacteria from some surfaces in this experimental model and may represent a better type of irrigation additive.